The invention relates to an electrical drive arrangement.
EP 73 503 B1 describes a motor control system in which the motor, which is a brushless d.c. motor, comprises stator windings, a permanent-magnet rotor and a position sensor to detect the position of said rotor relative to the stator windings, and in which an exciting current generation circuit is responsive to the position signal supplied by the position sensor and is capable of applying sinusoidal exciting currents to the stator windings. The frequency of the sinusoidal exciting currents is then controlled in accordance with the position signal in order to obtain a rotating field in synchronism with the rotation of the rotor. In order to control the phase of the sinusoidal exciting current for dynamically controlling the angle between the rotating magnetic field generated by the stator windings and the rotor position there has been provided a torque angle control circuit coupled to the exciting current generation circuit. The control system further comprises a tachometer coupled to the rotor to detect the rotor speed, the tachometer being coupled to the torque angle control circuit in such a manner that the phase of the sinusoidal exciting current varies in dependence on the rotor speed. The position sensor particularly supplies digital signals representative of the rotor position and the tachometer accordingly supplies signals representative of the rotor speed. Torque angle factors have been stored in a memory and there have been provided means to select torque angle factors in this memory in accordance with the digital rotor speed signals and to add the selected torque angle factor to the digital rotor position signal, in order to derive a signal for the excitation vector position. The known motor control system further comprises exciting current generation means by which the windings can be energized with sinusoidal exciting currents whose values are proportional to the sinusoidal values, which are incrementally controlled in conformity with the excitation vector position signal.
DE 41 36 538 A1 describes a commutator circuit for a brushless d.c. motor with trapezoidal drive, in which the commutation pulses of the commutation encoder of the brushless d.c. motor can be optimized in that the commutation pulses are advanced while at the same time the commutation pulse width is optimized. This is in order to enable a maximum efficiency or a maximum power and a maximum torque of the motor to be obtained over the entire range of motor speeds and the entire range of motor loads. This commutation uses inter alia a ROM address section with a presettable up-counter, which counts up clocked by the output signal of a binary counter and which for each reference commutation pulse is preset with the advance commutation angle as preset value in accordance with the prevailing angular velocity of the motor and the load current, which is read into a ROM, which has been loaded with data formed by the advance commutation angle of the commutation pulse, under control of the output signal of an address section, which supplies an address signal to the ROM.
The motor control system in accordance with EP 73 503 B1 requires a very accurate resolution of the digital signals representing the rotor position, which resolution should be at least 8 bits. The commutator circuit in accordance with DE 41 36 538 A1 comprises extensive memory circuits and address sections for these memory circuits.